The Twitter app, with its one-column tweet stream, now just got a sidebar with extra information. Now you can see more info, like individual tweets, people's profiles, videos, photos and various "media" providers that you can see in-line.
Also new! Keyboard shortcuts. Unlimited scrolling of your tweet stream.
It's launching today for a subset of Twitter users, in all the languages they support. It'll be an incremental rollout, and they don't know how long it will be before everyone gets it. [Twitter]
Update: Just changed the image to a screenshot of the new interface.
Oh, and if you want to follow me, here ya go.
Commenter Habs found this YouTube video showing the new Twitter that they just showed us.